Digital video discs (DVDs) allowing high-density recording with a large capacity and DVD devices for reproducing DVDs have been commercially available at present and received attention as products growing in demand. Since DVDs allow high-density recording, AlGaInP semiconductor lasers having an emission wavelength of 650 nm are used as laser light sources for recording/reproducing DVDs. Thus, the optical pickups of conventional DVD devices cannot reproduce compact discs (CDs) and Mini Discs (MDs) which are reproduced using AlGaAs semiconductor lasers having an emission wavelength of 780 nm.
In order to solve this problem, an optical pickup is used in which laser chips are incorporated into separate packages which include an AlGaInP semiconductor laser having an emission wavelength in the 650 nm band and an AlGaAs semiconductor laser having an emission wavelength in the 780 nm band. However, the optical pickup including the two packages of the AlGaInP semiconductor laser and the AlGaAs semiconductor laser has a large size, increasing the size of the DVD device. In order to solve this problem, an integrated semiconductor laser is provided in which two or more kinds of semiconductor lasers have different emission wavelengths and a light-emitting device structure is formed of semiconductor layers grown on the same substrate.
Referring to FIG. 13, such a conventional multi-wavelength semiconductor laser will be discussed below.
FIG. 13 is a perspective view showing the structure of a conventional multi-wavelength semiconductor laser.
As shown in FIG. 13, in the conventional multi-wavelength semiconductor laser, an AlGaAs semiconductor laser LD1 having an emission wavelength in the 700 nm band (for example, 780 nm) and an AlGaInP semiconductor laser LD2 having an emission wavelength in the 600 nm band (for example, 650 nm) are integrated separately on the same n-type GaAs substrate 201. The n-type GaAs substrate 201 is, for example, a substrate having a plane direction (100) or a substrate having a principle plane is off from the plane (100) by, for example, 5 to 15°.
In the AlGaAs semiconductor laser LD1, an n-type GaAs buffer layer 211, an n-type AlGaAs clad layer 212, an active layer 213 having a single quantum well (SQW) structure or a multiple quantum well (MQW) structure, a p-type AlGaAs clad layer 214, and a p-type GaAs cap layer 215 are sequentially stacked on the n-type GaAs substrate 201. The upper part of the p-type AlGaAs clad layer 214 and the p-type GaAs cap layer 215 are shaped like a stripe extending in one direction. An n-type GaAs current constriction layer 216 is provided on both sides of the stripe and forms a current constriction structure. On the stripe-like p-type GaAs cap layer 215 and the n-type GaAs current constriction layer 216, a p-side electrode 217 is in Ohmic contact with the p-type GaAs cap layer 215. The p-side electrode 217 is, for example, a Ti/Pt/Au electrode.
In the AlGaInP semiconductor laser LD2, an n-type GaAs buffer layer 221, an n-type AlGaInP clad layer 222, an active layer 223 having an SQW structure or an MQW structure, a p-type AlGaInP clad layer 224, a p-type GaInP intermediate layer 225, and a p-type GaAs cap layer 226 are sequentially stacked on the n-type GaAs substrate 201. The upper part of the p-type AlGaInP clad layer 224, the p-type GaInP intermediate layer 225, and the p-type GaAs cap layer 226 are shaped like a stripe extending in one direction. An n-type GaAs current constriction layer 227 is provided on both sides of the stripe and forms a current constriction structure. On the stripe-like p-type GaAs cap layer 226 and the n-type GaAs current constriction layer 227, a p-type electrode 228 is in Ohmic contact with the p-type GaAs cap layer 226. The p-type electrode 228 is, for example, a Ti/Pt/Au electrode.
On the back side of the n-type GaAs substrate 201, an n-side electrode 229 is in Ohmic contact with the n-type GaAs substrate 201. The n-side electrode 229 is, for example, an AuGe/Ni electrode or an In electrode.
In this case, the p-side electrode 217 of the AlGaAs semiconductor laser LD1 and the p-side electrode 228 of the AlGaInP semiconductor laser LD2 are respectively soldered on heat sinks H1 and H2 which are electrically separated from each other on a package base 300.
In the conventional multi-wavelength semiconductor laser configured thus, the AlGaAs semiconductor laser LD1 can be driven by passing current between the p-side electrode 217 and the n-side electrode 229 and the AlGaInP semiconductor laser LD2 can be driven by passing current between the p-side electrode 228 and the n-side electrode 229. Laser light having a wavelength of the 700 nm band (for example, 780 nm) can be extracted by driving the AlGaAs semiconductor laser LD1, and laser light having a wavelength of the 600 nm band (for example, 650 nm) can be extracted by driving the AlGaInP semiconductor laser LD2. The AlGaAs semiconductor laser LD1 and the AlGaInP semiconductor laser LD2 can be selectively driven by the switching of external switches and the like.
As described above, the conventional multi-wavelength semiconductor laser has the AlGaAs semiconductor laser LD1 having an emission wavelength in the 700 nm band and the AlGaInP semiconductor laser LD2 having an emission wavelength in the 600 nm band, and thus laser light for DVDs and laser light for CDs and MDs can be separately extracted. Therefore, DVDs, CDs, and MDs can be all reproduced or recorded by installing the multi-wavelength semiconductor laser as a laser light source in the optical pickup of a DVD device. The AlGaAs semiconductor laser LD1 and the AlGaInP semiconductor laser LD2 form a laser structure including the semiconductor layers grown on the same n-type GaAs substrate 201, so that only a single package of the integrated semiconductor laser is necessary. Thus the optical pickup can be minimized, reducing the size of the DVD device.